PHP | gmp_nextprime() Function

The gmp_nextprime() is an inbuilt function in PHP which is used to calculate the prime number just greater than a given GMP number(GNU Multiple Precision : For large numbers).

Syntax:

gmp_nextprime($num)

Parameters: This function accepts a GMP number $num as a mandatory parameter as shown in the above syntax whose next prime we want to find. This parameter can be a GMP object in PHP version 5.6 and later, or we are also allowed to pass a numeric string provided that it is possible to convert that string to a number.

Return Value: This function returns a GMP number which is the prime number just greater than the GMP number passed to it as a parameter.

Examples:

Input : gmp_nextprime("15")
Output : 17

Input : gmp_nextprime("21")
Output : 23

Below programs illustrate the gmp_nextprime() function in PHP :

Program 1: Program to calculate the prime number just greater than a GMP number when numeric string as GMP number is passed as an argument.

<?php
// PHP program to calculate the prime number greater
// than that of a GMP number passed as arguments

// strings as GMP numbers
$num = "135";

// gives the prime number just greater
// than 135 as a GMP number
$res = gmp_nextprime($num);

echo $res;

?>

Output:

137

Program 2: Program to calculate the prime number greater than that of a GMP number when GMP number is passed as an argument.

<?php
// PHP program to calculate the prime
// number greater than that of a GMP number

// creating GMP numbers using gmp_init()
$num = gmp_init(1000);

// gives the prime number just greater
// than 1000 as a GMP number
$res = gmp_nextprime($num);

echo $res;

?>

Output:

1009

Reference:
http://php.net/manual/en/function.gmp-nextprime.php